Cadillac Powertrain Control Module (PCM) Tuning Discussion, Pushing the envolope on mpg through tuning in Cadillac Engine Technical Discussion; Ok, in my experiments, I have done lots and lots of tuning. But for mpg, nothing REALLY has shown any ...

Pushing the envolope on mpg through tuning

Ok, in my experiments, I have done lots and lots of tuning. But for mpg, nothing REALLY has shown any big improvements.

Until now....

One thing that I tend to avoid, but it DOES seem to help.

Open loop cruise. As you might know, I do LOTS of detailed mpg evaluations. I average around 17.6 lately (last 4 tanks of gas been dead on 17.58-17.61). Now with OL Cruise I am, amazingly enough, at 20.23. Same drive, some bad weather tossed in (rain, fog, putzy traffic) and over 600+ miles it only needed 30 gallons of 87 octane.

Can't say for sure if it is legal (likely not....) but there is some serious merit for fuel economy here.

I'll probably run like 4 tanks with OL criuse, then back to 4 tanks in normal cruise and see how it compares.

Re: Pushing the envolope on mpg through tuning

Mostly, mainly keeping it from using the O2 sensors.

My theory is that I am not gross polluting. Why? I have well tuned VE Tables.
So if the O2 sensors ARE working properly as I have tuned, and then running the AFR as I have been, then my Open Loop AFR table values should be reasonably correct. The only pollutant I can be being excessive on is NOx. And being I don't run EGR, but DO run more limited cruise timing, I would bet it isn't much more than with everything being correct.

I could be seeing some higher HC if I am pushing it leaner than 14.67, but likely much less CO.

If I can get the $ to go have an emissions test done with the combinations I am testing would be very interesting (I have at least 4 combinations I want to test). I don't need emissions cert. I just need a analysis on my ride to see how I am doing.

Re: Pushing the envolope on mpg through tuning

N0DIH,

I assume you are tuning the PCM firmware to do this, not just cheating/bypassing the O2 sensors to keep in in OL mode? I ask because my 4.9 (which we have already had some posts on back and forth) is not getting decent MPG's IMHO. I'm averaging about 15.5-16, though more city miles than highway at the moment.

Obviously, you are doing a different powertrain on your FWB than I have on my SDV, but I am wondering if I might expect similar gains with a like setup on the 4.9, assuming it could be done. If so, I would be more inclined to put out the $ to get a programmer and dump the prom for you to play around with a bit sooner than I had been planning (what with budget constraints at the moment). Alternatively, I could buy a spare PCM (rather cheaply I'm sure, not much demand) and send you the PROM if you have facilities to read it out.

I will follow this thread to see what you find on the emissions impact of this setup. Here in MO, our emission cert program is set to change by the end of 2007 to exclude pre-OBDII (1996 model year) vehicles, so I could squeak by with a similar re-tuning after that. Of course, I don't want to be spewing a lot of NOx or HC's (or anything else) even if I can get better mileage. I try to be responsible anyway.

Re: Pushing the envolope on mpg through tuning

You might have a "highway mode" enable that will let you run at 17:1 or leaner at highway speeds.

You can easily pick up a few mpg with that, but you should be running significantly more timing to compensate for the faster burning mix. If there is no "highway mode", then it won't be worth trying it manually. I think you're talking about an LT1 right?

Re: Pushing the envolope on mpg through tuning

I think you are missing the boat on this. Do you have the AIR pump still on the car. It does not need to be on the car. TSB or Recall to remove. If you monitor the timing what happens in closed loop? The Dist will rattle and back down the timing. The LT1 is know to have rattles and retard timing. Do you have 4 wire O2 sensors on the car? I install them in place of a single wire sensor on most GM car ant trucks. You can almost double the MPG on a big block with a sensor upgrade. I simply install a relay on the heater circuit and then just hook up the Purple to The purple and the two grounds. Just think you have an old tank "94 Suburban 454" 7-8 MPG and I can make it about 15 MPG. WOW. I have done a lot of them. I have installed them on Carburated 307 & 305 Big cars with similar results.

Re: Pushing the envolope on mpg through tuning

Mine is a 94, not legal to pull AIR pump, that was 95-96. I had it disabled for a short time as it blew the fuse once not sure why. But it hasn't done it since, so I turned it all back on with no ill effects. The 94's had different check valves.

I have seen no issues at all on the LT1 with pinging for no reason and pulling back timing. I have hundreds of megs of datalogs, I would have caught it by now. No random pings on the KS's. People toss in the LT4 KM and it is not the right thing to do, it numbs the sensors so you don't hear it. Properly tuned is the key not faking it out. That is old school....

Yes, all LT1's have 4 wire sensors. As does my 99 K2500 454. I wish it would do 15 mpg, I have seen a friend of mine with one that he claimed it, but I never personally saw it do 15.

I always wanted to convert my 85 350 Olds Cutlass (was 307) to a 4 wire sensor, but never did.

Got a tank a E85 through, 16.18 mpg. Not too shabby for a alky burner! The LT1 really lends itself well to E85 with the high compression.

Re: Pushing the envolope on mpg through tuning

[QUOTE=N0DIH;1057362]Mine is a 94, not legal to pull AIR pump, that was 95-96. I had it disabled for a short time as it blew the fuse once not sure why. But it hasn't done it since, so I turned it all back on with no ill effects. The 94's had different check valves.

I have seen no issues at all on the LT1 with pinging for no reason and pulling back timing. I have hundreds of megs of datalogs, I would have caught it by now. No random pings on the KS's. People toss in the LT4 KM and it is not the right thing to do, it numbs the sensors so you don't hear it. Properly tuned is the key not faking it out. That is old school....

Cause
Under high engine speed and load conditions, hot exhaust gasses may leak past the AIR check valves. As the exhaust gasses in the in the air tube cool, water vapors collect into the AIR Pump. When the vehicle is driven, condensation from the AIR Pump may come into contact with the mass air flow sensor. This condition may cause a hesitation on acceleration and may also set the DTC.

Correction
Verify AIR Pump operation using a scan tool. Inspect the AIR Pump for traces of water. If the AIR Pump shows indication of water intrusion, install an AIR Pump service kit.

Important: Inspect the AIR check valves by using a hand vacuum pump. Apply 10 inches of vacuum to the AIR hose side of the check valve. Vacuum should hold for at least 10 seconds. If not, replace the AIR check valves.

Cause
Under high engine speed and load conditions, hot exhaust gasses may leak past the air check valves. As the exhaust gasses in the air tube cool, water vapors collect into the AIR pump. As the vehicle is driven, condensation from the AIR pump may come into contact with the Mass Airflow Sensor through the AIR inlet hose. This condition may cause a hesitation on acceleration and may also set the DTCs.

Correction
To correct this condition, a Secondary AIR Injection Pump disable procedure has been developed. (It has been determined that the Secondary AIR Injection system is not required to meet emission requirements for these vehicles only.)

I see you point. You most have it because why. It is 100% illeagal to alter the OEM calibration in the PCM

Re: Pushing the envolope on mpg through tuning

I don't think there is any laws that say it is illegal to change the OEM calibration of the PCM, if there was, the EPA would come down on HPTuners, TunerCat and EFILive and the like like a ton of bricks. But disabling a required emissions device is. Changing the calibration (timing, WOT fueling, etc) doesn't necessarily equate to bad emissions, the nature of the OBD1 emissions system protects that by itself. NOx might go up or down based on timing, but the actual amount of CO, CO2 or HC would be minimally changed.

Being in 94 it IS still required to have the AIR pump, the 95-96 it is not, as GM recertified it without. But didn't (why I don't know) include the 94. That is sort of puzzling. Probably because there are some differences in the 94 AIR system as compared to the 95-96, it might have taken a significant change in the application (probably a paperwork shuffle really).

There isn't any HP to be gained/list by the AIR pump removal, and it is only used in cold start and at WOT. But not any other time.

Re: Pushing the envolope on mpg through tuning

Originally Posted by N0DIH

There isn't any HP to be gained/list by the AIR pump removal, and it is only used in cold start and at WOT. But not any other time.

I see you did not read the TBS's completely. I have found most of the cars with bad AIR pump to have failed because of water in them. It is that water that sprays the MASS sensor. The water comes from leaking check valves. That would mean your AIR system is now an EGR system. Exhaust gas leaves the manifold and enters the air intake just before the MASS sensor.